The invention relates to a device for casting a ring-shaped plastic frame in a recess or annular recess of a rotor disk of a double-sided machining machine, The recess serves to hold a workpiece in the double-sided machining machine during the double-sided machining process. The device comprises two mold parts that accommodate the rotor disk between themselves, and a mold core that partially fills in the recess when the rotor disk is accommodated between the mold parts, wherein the mold core has at least one casting channel. One end of the mold terminates in a mold volume provided for the plastic frame and the other end is connectable to a supply for plastified plastic. The invention also relates to a corresponding method. Finally, the invention relates to a rotor disk of a double-sided machining machine.
A double-sided rotor disk is known for example from DE 102 28 441 B4. The rotor disks generally have a plurality of recesses in which workpieces, in particular semiconductor wafers, are held floating during machining in the double-sided machining machine. Suitable kinematics cause the rotor disks to move between the working gap formed between the machining disks such that they describe cycloid paths through the working gap in the semiconductor wafers held in the recesses of the rotor disks. The rotor disks normally consist of wear-resistant materials such as metal. To keep the semiconductor wafers from being damaged, the edge of the recesses of the rotor disks is normally provided with a plastic frame which is cast in the contour edge of the rotor disks in a casting procedure, such as a plastic injection molding procedure.
Extremely high demands are placed upon the dimensions of the semiconductor disks, such as silicon wafers, to be generated. These dimensions are significantly influenced by the consumable materials used during machining. For example in the case of double-sided polishing, be it abrasive polishing or haze-free polishing, the tolerances for global parallelism (GBIR), local flatness (SFQR), edge flatness (ESQFR) and the curvature of the top and bottom side of the wafer at the semiconductor edge (ZDD) are becoming increasingly smaller. The rotor disks and in particular the plastic frames play a decisive role since they influence the interaction between a polishing cloth applied to the working disks and the wafer edge. The plastic frame interacts with the polishing cloth depending on its thickness with reference to the semiconductor thickness, which in turn influences the polishing pressure at the edge of the wafer. For example, strong polishing cloth compression due to the plastic frame yields weak pressure by the polishing cloth on the wafer edge and vice versa.
For specific workpiece dimensions, in particular at the workpiece edge, the precise arrangement and dimensions of the plastic frame are highly important. With the known method, critical parameters such as the alignment of the plastic frame relative to the rotor disk main body, and hence a specific step height between the rotor disk and plastic frame, cannot be controlled in the desired manner. This can produce axially asymmetrical plastic frames with reference to the rotor disk. This in turn causes an uneven curvature of the semiconductor wafer edges after machining and hence an impairment of the local flatness. A spread of the frame dimensions, in particular the frame thickness occurring in known methods for producing plastic frames yield undesirable deviations in the dimensions of the semiconductor wafers machined in the machine. During the known casting methods, deviations in dimensions arise, for example due to the shrinkage of the material used and the parameters used in the casting method.